RFID integrated circuits with large contact pads

ABSTRACT

Technologies are generally directed to assembly of a Radio Frequency Identification (RFID) tag precursor. An assembly may be provided, the assembly having an RFID integrated circuit (IC), a nonconductive repassivation layer on a surface of the IC and confined within a perimeter of the surface, and a conductive redistribution layer on the repassivation layer and confined within the perimeter of the surface, in which a first portion of the redistribution layer is electrically connected to the IC through a first electrical connection. A substrate having a first antenna terminal to the assembly may be attached with an adhesive, and at least a first portion of a nonconductive barrier present on at least one of the first antenna terminal and the first portion of the redistribution layer may be reacted with a reactant to make the first portion of the nonconductive barrier conductive. A second electrical connection may then be formed between the first antenna terminal and the first portion of the redistribution layer through the first portion of the nonconductive barrier.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/776,346 filed on Feb. 25, 2013 by the same inventors, commonlyassigned herewith.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used to inventory, locate, identify,authenticate, configure, enable/disable, and monitor items to which thetags are attached or in which the tags are embedded. RFID systems may beused in retail applications to inventory and track items; in consumer-and industrial-electronics applications to configure and monitor items;in security applications to prevent loss or theft of items; inanti-counterfeiting applications to ensure item authenticity; and inmyriad other applications.

RFID systems operate by an RFID reader interrogating one or more tagsusing a Radio Frequency (RF) wave. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near field. The RF wave mayencode one or more commands that instruct the tags to perform one ormore actions.

A tag that senses the interrogating RF signal may reply with aresponding RF signal (a response). The responding RF signal may begenerated by the tag, or it may be formed by the tag reflecting back aportion of the interrogating RF signal in a process known asbackscatter. Backscatter may take place in a number of ways.

The reader receives, demodulates, and decodes the response. The decodedresponse may include data stored in the tag such as a serial number,price, date, time, destination, encrypted message, electronic signature,other attribute(s), any combination of attributes, or any other suitabledata. The decoded response may also encode status information about thetag, the item to which the tag is attached, or the item into which thetag is embedded such as a tag status message, item status message,configuration data, or any other status information.

An RFID tag typically includes an antenna and an RFID integrated circuit(IC) comprising a radio section, a power management section, andfrequently a logical section, a memory, or both. In some RFID ICs thelogical section includes a cryptographic algorithm which may rely on oneor more passwords or keys stored in tag memory. In earlier RFID tags thepower management section often used an energy storage device such as abattery. RFID tags with an energy storage device are known asbattery-assisted, semi-active, or active tags. Advances in semiconductortechnology have miniaturized the IC electronics so that an RFID tag canbe powered solely by the RF signal it receives. Such RFID tags do notinclude a long-term energy-storage device and are called passive tags.Of course, even passive tags typically include temporary energy- anddata/flag-storage elements such as capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Some embodiments are directed to RFID tag assembly. An RFID IC assemblyhaving a repassivation layer and a conductive redistribution layer maybe assembled onto a tag substrate with an additional layer. Theadditional layer may include one or more etchants or reactants forforming an electrical connection through a nonconductive barrier layerbetween the assembly and the substrate, and may also include an adhesivefor attaching the assembly to the substrate. Other embodiments may bedirected to patterned and/or nonoverlapping contact areas on an IC, ICself-assembly using liquids or other forces, and/or IC testing.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying Drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram of an assembled RFID tag.

FIG. 4 illustrates different IC contact pad configurations according toembodiments.

FIG. 5 illustrates an example capacitively-coupled inlay construction.

FIG. 6 illustrates an example galvanically-coupled inlay construction.

FIG. 7 illustrates a cross section of a capacitively-coupled inlayfollowing a thermal bonding step according to embodiments.

FIG. 8 illustrates the cross section of a capacitively-coupled inlaywith an overlay PET layer for additional strength according to oneembodiment.

FIG. 9 illustrates a conceptual diagram of an assembled RFID tag similarto the diagram of FIG. 2 employing assembly methods according toembodiments.

FIGS. 10A and 10B illustrate tag precursors having ICs galvanicallyconnected to antenna terminals on tag substrates according toembodiments.

FIG. 11 depicts repassivation layers on an IC according to embodiments.

FIG. 12 depicts patterned contact areas according to embodiments.

FIG. 13 depicts nonoverlapping or offset contacts according toembodiments.

FIG. 14 illustrates a tag assembly method according to embodiments.

FIGS. 15A and 15B illustrate wafer-scale probe testing of ICs accordingto embodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustrations specific embodiments or examples. These aspects maybe combined, other aspects may be utilized, and structural changes maybe made without departing from the spirit or scope of the presentdisclosure. The following detailed description is therefore not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generate signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals).

Reader 110 and tag 120 communicate via signals 112 and 126. Whencommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1. Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which is preferably implemented asan IC 224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable antenna contacts(not shown in FIG. 2).

IC 224 is shown with a single antenna port, comprising two antennacontacts electrically coupled to two antenna segments 227 which areshown here forming a dipole. Many other embodiments are possible usingany number of ports, contacts, antennas, and/or antenna segments.

In operation, the antenna receives a signal and communicates it to IC224, which both harvests power and responds if appropriate based on theincoming signal and the IC's internal state. If IC 224 uses backscattermodulation then it responds by modulating the antenna's reflectance,thereby generating response signal 126 from signal 112 transmitted bythe reader. Electrically coupling and uncoupling the antenna contacts ofIC 224 can modulate the antenna's reflectance, as can varying theadmittance of a shunt-connected circuit element which is coupled to theantenna contacts. Varying the impedance of a series-connected circuitelement is another way to modulate the antenna's reflectance.

In the embodiment of FIG. 2, antenna segments 227 are separate from IC224. In other embodiments the antenna segments may be formed on IC 224.Tag antennas according to embodiments may be designed in any form andare not limited to dipoles. For example, the tag antenna may be a patch,a slot, a loop, a coil, a horn, a spiral, or any other suitable antenna.

FIG. 3 is a conceptual diagram of an assembled RFID tag. An RFID ICincludes electrical circuit elements (e.g. active RF circuits 316) andconnecting traces. The IC may include multiple layers containing RF andnon-RF circuits. Electrical connections for RF circuits may be coupledto an RF distribution bus 324 through coupling capacitors 326. Non-RFtraces 318 may be separated from the RF traces (e.g., the RFdistribution bus 324).

The antenna of tag 300 is illustrated in FIG. 3 as antenna trace 1 (320)and antenna trace 2 (322). The antenna is typically formed as a thintrace of metal—e.g. aluminum or copper—affixed onto the IC with one ormore connection points for connecting the antenna to the RF circuits(through RF distribution bus 326). When an oxidizing metal like aluminumis used, a naturally forming oxide layer 324 creates a hard surfacebetween the antenna traces and the IC.

One disadvantage of many tag assembly methods is that the antenna layerhas to be accurately aligned with the IC to ensure that the antenna isproperly coupled to the RF distribution bus. In these assemblytechniques, the antenna connections are commonly aligned with the RFdistribution bus using a gold or similarly-topped bump 312 appliedthrough a post-processing step. Even so, assembly may be ratherdifficult because it requires tightly-controlled mounting forces andhigh-precision IC placement.

Certain assembly methods may also result in IC performance reductionsdue to RF distribution bus resistance and parasitic capacitance (330)between non-RF IC traces 318 and antenna traces 320/322. The highmounting force used for IC bump 312 to penetrate the hard antenna oxidelayer 324 to contact the antenna trace 320 may lead to reliability andyield problems. In addition, such high mounting forces may alsoexacerbate parasitic capacitance effects by reducing separation distancebetween the antenna traces and the IC surface.

Conductive adhesives (e.g. isotropic or anisotropic conductor pasteadhesive) can be used to alleviate some of these disadvantages, butadhesives may introduce other complications. For example, many adhesivesmay limit tag assembly throughput because they must be applied inviscous fluid form immediately prior to IC placement and requirecontinuous pressure and heat to cure.

FIG. 4 illustrates different IC contact pad configurations according toembodiments. In configuration 440. IC 430 has four contact pads (432),which may be openings in a passivation layer covering a metal layer onIC 430. Configuration 442 shows the same IC configuration with bumps(e.g. gold bumps) 439 added during a post-processing step and antennapads 438 over the bumps. The bumps 439 may be added for alignmentpurposes (as discussed above) and to allow external contact to thecontact pads 432, which may be recessed within the covering passivationlayer.

To address some of the disadvantages of bump addition and IC-antennaalignment described above, one or more relatively large contact pads(e.g. 434, 436) may be formed on a top surface of the IC 430 instead ofsmall contact pads 432, as shown in configurations 444 and 446. Theselarge contact pads form a top layer of the IC and provide a capacitiveor galvanic coupling mechanism to the tag antenna. Large contact padsprovide more area for coupling to a tag antenna, and as a result, reduceparasitic capacitances and the need for accurate alignment. The largecontact pads may cover a significant portion of the top surface of theIC 430. For example, the large contact pads may cover more than 20%,30%, 40%, 50%, 60%, 70%, 80%, 90%, or even up to 100% of the top surfaceof the IC 430. In some embodiments, the large contact pads 434/436 maybe formed on a dielectric or repassivation layer on the IC 430 and thenelectrically connected to contact pads below the dielectricrepassivation layer (e.g., contact pads 432). While the particular largecontact pads 434/436 in FIG. 4 are shown as substantially rectangular,large contact pads do not need to be rectangular, and may have anysuitable shape. For example, a large contact pad may be circular orannular.

When using large contact pads for capacitive connections to antennas,the capacitance between the large contact pads and the antenna tracesmay be controlled by adjusting the dielectric characteristics (e.g.composition, thickness) of material disposed between the IC and theantenna, such as non-conductive material covering the pads,non-conductive material covering the antenna traces (e.g. a naturallygrown or enhanced oxide layer on aluminum traces), and/or any additionaldielectric material. Galvanic connections may also be provided bypressing an antenna onto the IC such that one or more “dimples” formedon the antenna traces make direct contact with one or more large contactpads on the IC. In some embodiments, as described below, galvanicconnections may also or instead be accomplished without dimples, bumps,or other raised regions.

FIG. 5 illustrates an example capacitively-coupled inlay construction.IC 552 in diagram 500 is shown with a single large contact pad 554.While the large contact pad(s) according to preferred embodiments covera substantial portion of the IC surface, embodiments are not so limited,and larger or smaller pads may also be implemented using the principlesdescribed herein. In some embodiments, the combined area of all contactpads on a particular surface of the IC does not exceed the area of thatparticular surface, and any contact pads on that surface are confinedwithin or extend up to that surface's perimeter. Of course, in otherembodiments, contact pads may extend out beyond the perimeter of an ICsurface. For example, contact pads may wrap around or encroach ontoneighboring IC surfaces, or even extend outward from the IC surface in acantilevered fashion.

First, a tag antenna may be formed by depositing a conductive antennatrace pattern 556 on a dielectric 558 such as polyethylene terephthalate(PET). Other dielectric materials may also be used, including but notlimited to Mylar, polypropylene (PP), polystyrene (PS), polyester,polyimide (PI), or vinyl. The IC and the antenna may then be broughtinto proximity to form a capacitive connection. For example, the IC maybe heated to the plasticity temperature of dielectric 558, and thensubsequently pressed into the dielectric to achieve a predefinedthickness between pad 554 and antenna traces 556 (within giventolerances).

Thus, a method of tag assembly according to one embodiment includesaffixing the antenna to the IC by forming at least one capacitor havinga dielectric material and coupling the antenna to the IC. The dielectricmaterial may include an IC covering layer, an antenna covering layer,and/or other dielectric layers. The covering layers may include anon-conductive layer disposed over an IC top metal layer (e.g., thelarge contact pads), an antenna dielectric layer (e.g., anaturally-occurring or grown metal oxide or nitride layer, for metallicantennas). Other dielectric layers may include adhesive materials withcontrollable dielectric characteristics. The thickness of the dielectricmaterial may vary depending on the dielectric characteristics of thematerial and a desired minimum capacitance, and in some embodiments maybe between 5 nm to 1 μm, inclusive.

As discussed above, in some embodiments large contact pad(s) on an ICsurface may substantially cover the entire IC surface. In cases wheremultiple large contact pads exist, multiple capacitors may be formed,where each distinct capacitor may be coupled to distinct electricalcircuits of the IC such as a rectifier circuit, a demodulator circuit,or a modulator circuit, thus enabling these circuits to be at differentDC potentials. According to other embodiments, another antenna terminalmay be affixed to a second surface of the IC (opposite the firstsurface) forming another capacitor (or set of capacitors) on the surfaceof the chip. In cases with multiple capacitors (and/or two-sidedcoupling), one or more connections may be galvanic by providing a directcontact between the antenna trace and one or more large contact pads onthe IC.

FIG. 6 illustrates an example galvanically-connected inlay construction.First, an antenna may be formed by depositing a conductive pattern 674on a surface of a non-conductive material such as PET 672 as shown indiagram 670. Subsequently (e.g. following an embossing process), a smalldimple (e.g. approximately 30 μm in diameter) 684 may be placed on theconductive pattern 674, which typically results in a similar dimple onthe PET material as well (682) as shown in diagram 680. An IC 692 with alarge contact pad 698 may then be pressed onto the antenna (e.g., asdescribed above in relation to FIG. 5) as shown in diagram 690, to forma galvanic connection between the antenna 696 and the large contact pad698 at location 699.

FIG. 7 illustrates a cross section of a capacitively-coupled inlayfollowing a thermal bonding step according to embodiments.

As shown in diagram 700, an example tag assembly includes an IC 710inserted into dielectric (e.g. PET) 708 covering an antenna 706.Electrical coupling between IC 710 and antenna 706 is provided by one ormore capacitors formed between large contact pad(s) disposed on thesurface of IC 710 and antenna 706. The dielectric of the capacitor mayinclude a portion of dielectric 708, any non-conductive covering layerof IC 710, and/or an additional dielectric layer 712 between the IC 710and the antenna 706. In some embodiments, additional dielectric layer712 may include a naturally occurring or artificially grown oxide layerof antenna 706, an adhesive dielectric material, or other materials.

According to some embodiments an IC may not be directly coupled to theantenna, but rather coupled through an interposer layer. For example, astrap may be capacitively coupled to the IC as discussed above and theantenna later electrically coupled to the strap. Thus, the tag assemblymay include additional connection layers between the antenna and the ICusing the principles described herein.

In other embodiments, affixing the antenna to the IC may includeperforming an IC metal deposition and patterning process, subsequentlydepositing a passivation material comprising the dielectric material,singulating the IC from a completed wafer, and pressing the antenna, thedielectric material, and the IC together. The dielectric material mayinclude a material with a relatively high (e.g. >8) dielectric constantsuch as hafnium oxide, zirconium oxide, hafnium oxide silicate,zirconium oxide silicate, and strontium-titanium-oxide. Alternatively,the wafer process may be completed as is known in the art including thepassivation deposition and pad opening etch, and then the IC singulatedand pressed with the antenna and the dielectric material.

FIG. 8 illustrates a cross section of a capacitively-coupled inlay withan overlay layer for additional strength according to one embodiment.

The example tag assembly shown in diagram 800 is similar to the tagassembly shown in FIG. 7 with the addition of an overlay layer 814 addedfor enhanced strength. The overlay 814 may include PET and/or any othersuitable material, and may be affixed through adhesives or other meansdepending on the tag design and use. For example, the antenna layer maybe disposed directly onto a host item, the IC then pressed onto theantenna layer as discussed and the overlay layer 814 placed over the ICand antenna layer. The overlay layer may also be configured to provideother functions, such as being a writeable label, and the like.

FIG. 9 illustrates a conceptual diagram of an assembled RFID tag similarto the diagram of FIG. 3 employing assembly methods according toembodiments.

Diagram 900 illustrates differences between conventional tag assemblymethods and tag assembly methods according to embodiments. By employinglarge contact pads 940 on an IC surface, capacitive coupling betweenantenna traces (320, 322) and active RF circuits 316 is achieved. Thisreduces parasitic capacitance between non-RF traces 942 and antennatraces 320/322. Furthermore, since no RF distribution bus is needed. RFdistribution resistance is also eliminated.

The capacitors between the antenna traces and the IC circuits mayinclude an oxide layer 324 of the antenna traces and/or a covering layerof the antenna/IC as dielectric material. The dielectric characteristicsof these materials may be controlled through their composition andthickness (e.g. enhanced growth of the oxide layer, controlled thicknessof the dielectric layer, etc.), enabling tag designers to set predefinedcapacitance values.

Mechanical limitations such as the use of gold-topped bumps, accuratealignment, and controlled mount force are also significantly reducedsince the large contact pads may be implemented to be as large as the ICsurface. This results in fewer assembly steps and increased reliabilityand throughput.

As described above in relation to FIG. 6, an IC may be galvanically orconductively connected to the conductive trace of an antenna by, forexample, using a dimple on the trace to directly connect the trace to alarge contact pad on the IC. In some embodiments, an IC contact pad maybe galvanically connected to an antenna without the use of a dimple,bump, or raised region.

FIGS. 10A and 10B illustrate tag precursors having ICs galvanicallyconnected to antenna terminals on tag substrates according toembodiments. A tag precursor is a portion of a complete RFID tag, andincludes the RFID IC and either a substrate having the entire tagantenna (i.e., an inlay) or a substrate having only a portion of theentire tag antenna (i.e., a strap). In the latter case, the strap maythen be attached to an inlay.

FIG. 10A depicts an IC 1002 and a tag substrate 1008. IC 1002 includesone or more large contact pads 1004, similar to pads 334 and 336 in FIG.3, that electrically connect to one or more electrical circuit elementswithin IC 1002. Tag substrate 1008, which may be a strap or an inlay,includes an antenna terminal 1010, which may be a trace of metal similarto antenna traces 320 and 322 described in FIG. 3. If antenna terminal1010 includes an oxidizing metal such as aluminum or copper, an oxidelayer 1012 may form on terminal 1010, for example due to exposure toair. Oxide layer 1012, if allowed to remain, acts as an insulating layerwhich prevents the formation of a galvanic connection between IC pad1004 and antenna terminal 1010.

To address this issue, an additional layer 1006 may be added tofacilitate the formation of a galvanic connection between IC pad 1004and antenna terminal 1010. In some embodiments, additional layer 1006includes etchants for forming openings by etching or breaking throughoxide layer 1012. For example, additional layer 1006 may includeparticles (spherical, ovoid, angular, sharp-edged, etc.) that formopenings in the oxide layer 1012 by rupturing it when heat and/orpressure are applied. In one embodiment, particles suspended in afast-drying binder or liquid may be applied to the IC 1002 or thesubstrate 1008 and then dried to form the additional layer 1006.Additional layer 1006 may also (or instead) include agent(s) for etchingor reacting with oxide layer 1012 to form openings. For example, ifantenna terminal 1010 includes aluminum, additional layer 1006 mayinclude an etchant or solubilizing agent for aluminum oxide. When IC1002 with additional layer 1006 is disposed on antenna terminal 1010,components in additional layer 1006 (e.g., the particles and/or agentsdescribed above) create openings in oxide layer 1012, thus allowing ICpad 1004 to form a galvanic connection with antenna terminal 1010.

In some embodiments, the additional layer 1006 may include an adhesivefor attaching the IC 1002 to the tag substrate 1008. For example, theadhesive may include an isotropic or anisotropic conductive materialand/or a nonconductive adhesive. In some embodiments, the adhesive mayalso include one or more of the mechanical and/or chemical etchants orreactants described herein (e.g., particles, etchants, solubilizingagents, dopants, etc.), while in other embodiments the adhesive may beseparate from the etchant(s).

If the additional layer 1006 is electrically conductive, the galvanicconnection between IC pad 1004 and antenna terminal 1010 may be formedthrough the additional layer 1006. For example, if the additional layer1006 includes conductive particles for forming openings in the oxidelayer 1012, the conductive particles may help form the galvanicconnection. If the additional layer 1006 is not electrically conductive,it may be removed as a result of applied heat, pressure, or otherprocessing, thus allowing IC pad 1004 to directly contact antennaterminal 1010 to form a galvanic connection (e.g., after applyingpressure, heat, or some other processing). In some embodiments, the ICpad 1004 itself may have a textured surface (e.g., surfaceirregularities, ridges, protrusions, and/or other topological features)for etching or rupturing oxide layer 1012 when heat and/or pressure isapplied. For example, the IC pad 1004 may be fabricated to includerelatively sharp-edged ridges or bumps on its surface in a patterned orrandom arrangement. In some embodiments, laser-assisted etching or othermethods of selective etching may be used to provide surface texturing onthe IC pad 1004.

FIG. 10B depicts a diagram 1050 similar to diagram 1000 in FIG. 10A.However, instead of an oxide layer, a masking layer 1052 covers antennaterminal 1010. Masking layer 1052 may be deposited after antennaterminal 1010 is formed to serve as a protective layer that prevents theformation of an oxide layer on the antenna terminal. The masking layer1052 may include an organic or inorganic dielectric material, or mayeven include a metallic or other electrically-conductive material thatpreferably does not oxidize. If masking layer 1052 includes a dielectricor insulating material, additional layer 1006 may include agent(s) forreacting with, etching, or solubilizing masking layer 1052 and/orparticles that rupture masking layer 1052 when heat and/or pressure isapplied. If masking layer 1052 includes an electrically-conductivematerial, additional layer 1006 may include material for galvanicallyconnecting IC pad 1004 and masking layer 1052, or may not even bepresent.

While heat and/or pressure applied to an IC or a tag substrate may beused to form a galvanic connection (e.g., as described previously), insome embodiments processing other than heat and/or pressure may also beused to form a galvanic connection between IC pad 1004 and antennaterminal 1010. For example, an electric field may be applied between ICpad 1004 and antenna terminal 1010. The electric field may facilitateetching of any oxide layer (e.g., oxide layer 1012) by, for example,increasing the etching rate and/or the etching selectivity. The electricfield may also facilitate the physical formation of the galvanicconnection between IC pad 1004 and antenna terminal 1010 by, forexample, electronically welding the pad to the terminal or promotingelectromigration of metallic ions such that pad 1004 is electricallyshorted to terminal 1010. As another example, ultrasonic welding may beused to disrupt oxide layer 1012 and/or short pad 1004 to terminal 1010.

In some embodiments, reactants or agents in the additional layer 1006may react with the oxide layer 1012 or the masking layer 1052 to form aconductive pathway between IC pad 1004 and antenna terminal 1010 withouthaving to form openings in the oxide layer 1012 or the masking layer1052. For example, the masking layer 1052 may include a nonconductiveplastic. When the additional layer 1006 is in contact with the maskinglayer 1052, dopants in the layer 1006 may diffuse into portions of themasking layer 1052, turning those portions conductive and creating theconductive pathway. In some embodiments, heat and/or pressure may beused to facilitate the diffusion/reaction.

In some embodiments an IC may include a nonconductive repassivationlayer. The repassivation layer may cover a surface of the IC, bedisposed between the IC and a substrate (e.g., additional dielectriclayer 712 in FIG. 7), or be disposed between antenna contact pads andthe rest of the IC, as depicted below in FIG. 11. The repassivationlayer may aid in mitigating mounting capacitance variations due tovarying mounting forces, and may also reduce parasitic capacitivecoupling between large antenna contact pads and other IC circuitcomponents. In some embodiments, a repassivation layer is confinedwithin and/or extends up to the perimeter of the IC surface on which itis disposed. However, in other embodiments, the repassivation layer mayextend beyond the IC surface perimeter. For example, the repassivationlayer may wrap around or encroach onto one or more neighboring surfacesof the IC, or may extend out from the IC surface in a cantileveredfashion.

FIG. 11 shows a diagram 1100 in which an RFID strap or inlay comprisingsubstrate 1120 and antenna terminal 1127 is pressed against RFID IC 1124with a mounting force F1 (1102), where antenna terminal 1127 and contactlayer 1112 are separated from the IC by repassivation layer 1110.Mounting distance D1 (1104) is fixed by repassivation layer 1110,producing a similarly fixed mounting capacitance C1.

In some embodiments contact layer 1112, similar to contact pads 434 or436 in FIG. 4, substantially covers a large portion of the surface ofRFID IC 1124. The contact layer 1112 may include a conductive material,such as a metal or other material that is electrically conductive orpossesses metallic properties. In some embodiments, the contact layer1112 may be formed from a conductive redistribution layer applied ordeposited on the repassivation layer 1110. The conductive redistributionlayer may be applied by evaporation, sputtering, or direct transfer. Insome embodiments, the conductive redistribution layer may then bepatterned (e.g., to form contact pads, strips, or any desired contactshape) to form the contact layer 1112. For example, evaporation orsputtering of the redistribution layer may be accompanied with a maskingstep to define a desired contact pattern (e.g., with photoresist) and anetching step (if masking occurs after layer deposition) or aliftoff/removal step (if masking occurs before layer deposition). Insome embodiments, the contact layer 1112 may be applied to anothersubstrate, patterned, and then transferred to the IC. While one contactlayer 1112 is depicted in FIG. 11, in other embodiments more thancontact layer may be present, or the contact layer 1112 may includemultiple portions. For example, the contact layer 1112 on therepassivation layer 1110 may be patterned to provide multiple contactareas, each electrically disconnected from each other.

As with the repassivation layer 1110, in some embodiments the contactlayer 1112 is confined within and/or extends up to the perimeter of therepassivation layer 1110 and/or the IC surface upon which therepassivation layer 1110 is disposed. Of course, in other embodiments,the contact layer 1112 may extend out beyond the perimeter of therepassivation layer or IC surface. For example, contact layer 1112 maywrap around or encroach onto neighboring surfaces, or even extendoutward from a surface in a cantilevered fashion.

Diagram 1150 shows the RFID strap or inlay being pressed against theRFID IC with a mounting force F2 (1152) which is larger than mountingforce F. The presence of repassivation layer 1110 ensures that mountingdistance D2 (1154) is substantially the same as mounting distance D1(1104) despite the larger mounting force F2. As a result, mountingcapacitance C2 is substantially similar to mounting capacitance C1,helping ensure that the tags have similar tuning and therefore similarperformance characteristics.

In some embodiments, bumps 1108 formed through openings in repassivationlayer 1110 galvanically connect circuits 1162 to contact layer 1112. Inother embodiments, bumps 1108 may not be present. In this case, circuits1162 may either be capacitively or galvanically connected to contactlayer 1112 through the repassivation layer 1110. For example, if nosuitable conductive path exists through the repassivation layer 1110,circuits 1162 may capacitively connect to contact layer 1112. In someembodiments, the contact layer 1112 may be directly deposited onopenings in the repassivation layer 1110, thus galvanically connectingto circuits 1162. In other embodiments, portions of the repassivationlayer 1110 may be made conductive, as described above in relation to theoxide layer 1012/masking layer 1052 in FIGS. 10A-B, and galvanicconnections between circuits 1162 and contact layer 1112 made throughthe conductive portions.

Repassivation layer 1110 may be an organic or inorganic material,typically (although not necessarily) with a relatively low dielectricconstant and a reasonable thickness to provide small capacitance. Ananisotropic conductive adhesive, patterned conductive adhesive, ornonconductive adhesive 1113 may optionally be applied between the IC andthe strap/inlay to connect the IC to the strap/inlay, physically and/orelectrically. If adhesive layer 1113 is nonconductive then it istypically sufficiently thin such that at the frequencies of RFIDcommunications it provides a low-impedance capacitive path betweenantenna terminal 1127 and contact layer 1112.

In some embodiments, repassivation layer 1110 may include an air gapthat separates contact layer 1112 from IC 1124 to further decouple thetwo capacitively. The air gap may be bridged by support pillar(s)between contact layer 1112 and IC 1124 (including bumps thatelectrically connect the two). In some embodiments, the contact layer1112 may include a metallic or conductive mesh structure to facilitatethe formation of the air gap.

The contact layer 1112, being a relatively large metallic pad, may alsohelp to protect the underlying repassivation layer 1110 during ICfabrication. For example, contact layer 1112 may serve as an etch maskthat covers and prevents etching or damage to underlying portions ofrepassivation layer 1110 during processing like that described in U.S.Pat. No. 7,482,251 issued on Jan. 27, 2009, the entirety of which ishereby incorporated by reference.

As described above, in some embodiments a contact layer may includecontact areas having different shapes. FIG. 12 depicts patterned contactareas according to embodiments. Diagram 1200 depicts a top view of an IC1202 with IC contacts 1204 and 1206. The IC 1202 also has contact areas1208 and 1210 which overlie and electrically connect to IC contact pairs1204 and 1206, respectively. The contact areas 1208 and 1210 allow theIC contact pairs 1204 and 1206 to electrically connect to externalelectrical elements, such as antenna terminals on an RFID strap or inlay(e.g., antenna terminal 1127).

The contact areas 1208 and 1210 may be fabricated and shaped bypatterning a deposited conductive redistribution layer as describedabove in reference to FIG. 11. The shapes and/or orientations of thecontact areas may be based on aesthetics, ease of forming electricalconnections to antenna terminals, and/or coupling to components in theIC 1202. For example, the contact areas 1208 and 1210 may be shaped tominimize parasitic capacitive coupling with sensitive elements withinthe IC 1202. In these cases, the conductive redistribution layer may bepatterned such that portions of the redistribution layer whose localparasitic capacitance to the IC 1202 (or elements in the IC 1202) exceeda particular threshold are excised during the patterning process. Forexample, the portions may be removed after deposition using amask-and-etch process or prevented from being depositing in the firstplace using a mask-and-liftoff process. The threshold(s) may bepredefined prior to the patterning of the redistribution layer, and maybe determined based on, for example, a desired parasitic capacitance ofthe entire IC or a desired local parasitic capacitance of a portion ofthe IC.

Diagram 1250 depicts a top view of another embodiment of IC 1202. Indiagram 1250, only one contact from each of IC contact pair 1204 and1206 may be electrically connected to the contact areas 1208 and 1210.For example, this may be done to reduce capacitance between the contactareas and the IC contact pairs. Also as shown in diagram 1250, thecontact areas 1208 and 1210 may have curved or rounded edges. This maybe done to ease the masking, etching, and/or liftoff patterningprocesses.

In some embodiments, a contact location between a contact layer (e.g.,contact layer 1112 or contact areas 1208/1210) and antenna terminal(e.g., antenna terminal 1127) may differ from a contact location betweenthe contact layer and the IC (e.g., bump(s) 1108). FIG. 13 depictsnonoverlapping or offset contacts according to embodiments, and depictsa top view 1300 and a cutaway view 1350 (taken along the A-A′ axis shownin view 1300). In FIG. 13, an IC 1302 has IC contacts 1304 and 1306. Arepassivation layer 1320 is disposed over the IC contacts 1304 and 1306,and contact pads 1308 and 1310 are disposed on the repassivation layer1320. The contact pads 1308 and 1310 may be formed by patterning adeposited contact layer, as described above. The IC contacts 1304 and1306 are electrically connected through the repassivation layer 1320 tothe contact pads 1308 and 1310, respectively. As shown in view 1350. ICcontact 1306 may be electrically connected to contact pad 1310 via abump 1322 (similar to bump 1108) formed through an opening in therepassivation layer 1320. A similar bump (not shown) may electricallyconnect IC contact 1304 to contact pad 1308 through another opening inthe repassivation layer 1320. In some embodiments, the contact pads 1310and 1308 may directly electrically connect with the IC contacts 1306 and1304, respectively, without bumps. For example, the contact pads1310/1308 may be deposited on an opening in the repassivation layer1320, directly forming an electrical connection with underlying ICcontacts 1306/1304.

The contact pads 1308 and 1310 are further electrically connected toantenna terminals 1312 and 1314, respectively. In particular, contactpad 1308 electrically connects to antenna terminal 1312 through contactarea 1316, and contact pad 1310 electrically connects to antennaterminal 1314 through contact area 1318. If an oxide, masking, or othernonconductive layer covers the contact pads and/or the antennaterminals, openings may be formed at the contact areas 1316 and 1318before the electrical connections are made, as described above.

In some embodiments, contact pad/IC contact connections and contactpad/antenna terminal connections (and their respective openings in therepassivation layer and oxide/masking layer, if present) may be offsetfrom each other and nonoverlapping, as shown in FIG. 13. This mayprovide flexibility in terms of the placement of the IC onto the antennaterminals. Of course, in other embodiments the connections/openings maypartially overlap, or a connection (e.g., a contact pad/antenna terminalconnection) may wholly encompass another connection (e.g., a contactpad/IC contact connection).

Large IC contact pads as described herein may also assist in thepositioning of an IC on a substrate. FIG. 14 illustrates a top view 1400and a side view 1450 of a tag self-assembly method according toembodiments. In FIG. 14, an IC 1402 is to be deposited on a substratehaving antenna terminals 1408 and 1410. In particular, IC 1402 is to bedeposited such that first IC contact pad 1404 overlaps first antennaterminal 1408 (but not second antenna terminal 1410) and second ICcontact pad 1406 overlaps second antenna terminal 1410 (but not firstantenna terminal 1408).

Liquid surface tension may be used to facilitate the alignment of eachcontact pad with its respective antenna terminal. Surface tensionresults from cohesive forces between liquid molecules. When two dropletsof similar liquid (or liquids having similar surface energies) areplaced close to each other, they will tend to coalesce into a single,larger droplet in order to minimize the number of exposed molecules andthereby minimize surface energy. If the two droplets are each associatedwith a different object, the coalescence of the two droplets may alsopull the different objects together.

In FIG. 14, at least some of the contact pads and/or the antennaterminals may each be associated with a liquid droplet. For example,contact pad 1404 may be associated with droplet 1412, contact pad 1406may be associated with droplet 1414, antenna terminal 1408 may beassociated with droplet 1416, and antenna terminal 1410 may beassociated with droplet 1418. When IC 1402 is brought into closeproximity to the substrate (and antenna terminals 1408 and 1410),droplet 1412 may be attracted to droplet 1416, thus drawing IC pad 1404into contact with antenna terminal 1408. Similarly, droplet 1414 may beattracted to droplet 1418, drawing IC pad 1406 into contact with antennaterminal 1410.

In one embodiment, the liquid droplets 1412-1418 may include water. Insome embodiments, the liquid droplets may also include one or moreliquid adhesives, such as a conductive, nonconductive, oranisotropically conductive adhesive. Liquid droplets 1412-1418 mayresult from solid material. For example, a solid film or solid particlesmay first be deposited on the contact pads and/or the antenna terminals.The deposited solid material may then be heated, chemically modified, orotherwise processed to form the liquid droplets 1412-1418. For example,solid solder may initially be deposited on the contact pads and/or theantenna terminals. Just prior to the assembly process, heat may beapplied to IC 1402 and/or the substrate in order to melt the solidsolder into liquid solder droplets. Subsequently, IC 1402 may be broughtinto close proximity to the substrate (and antenna terminals 1408 and1410), and the liquid solder droplets on the IC contact pads and/or theantenna terminals may coalesce to draw the IC and the substratetogether. In some embodiments, IC 1402 may be brought into closeproximity to the substrate before heat is applied. Subsequently, heatmay be applied to melt the solid solder deposited on the contact padsand/or the antenna terminals, which causes contact pads and antennaterminals close to each other to be drawn together (via dropletcoalescence). Of course, solid materials other than solder may be used.

In some embodiments, different types of liquids may be used for eachpair of IC pad and antenna terminal. For example, a first type of liquidmay be placed on IC pad 1404 and antenna terminal 1408, and a secondtype of liquid may be placed on IC pad 1406 and antenna terminal 1410.The liquid types may be selected to have different surface tensionproperties, such that droplets of the first type of liquid do notattract droplets of the second type of liquid. For example, droplets ofa polar liquid (e.g., water) may be placed on IC pad 1404 and antennaterminal 1408, and droplets of a nonpolar liquid (e.g., an oil) may beplaced on IC pad 1406 and antenna terminal 1408. In some embodiments,substances that are liquid under different conditions may be used. Forexample, water droplets may be placed on IC pad 1404 and antennaterminal 1408, and solid solder may be placed on IC pad 1406 and antennaterminal 1410. When the IC is initially deposited on the substrate, ICpad 1404 and antenna terminal 1408 will be drawn together by theirassociated water droplets. Subsequently, the IC and substrate may beheated such that the solid solder on IC pad 1406 and antenna terminal1410 melt and draw the pad and terminal together.

While FIG. 14 depicts liquid droplets on each of the IC pads and antennaterminals, in some embodiments liquid droplets may be present on onlyone IC pad or antenna terminal in each pair of IC pads and antennaterminals. In these embodiments, the liquid droplet on the IC pad (orantenna terminal) may be preferentially attracted to the material of theantenna terminal (or IC pad). For example, a droplet of a polar liquid(e.g., water) may be preferentially attracted to a metal (e.g., themetal of an IC pad or antenna terminal).

Other techniques may also be used to assemble or align ICs onto antennaterminals on a substrate. As one example, electrostatic attraction maybe used to assemble an electrically-charged IC onto oppositely-chargedantenna terminals. The charge on the IC and/or antenna terminals may beinduced by a laser (e.g., as with laser printing) or by any othersuitable means.

In addition to facilitating IC placement on substrates, large IC contactpads as described herein may also facilitate IC testing. FIGS. 15A and15B illustrate wafer-scale probe testing of ICs according toembodiments. ICs on a wafer can be tested by using individual probes tocontact individual IC contact pads. In some embodiments, multiple testprobes are combined into a probe card, which serves as an interfacebetween the test system and the wafer. In order to test ICs on a wafer,the probe card (or individual probes) must be carefully aligned with ICcontact pads on the wafer. Large IC contact pads as described hereinsimplify the probe alignment process, because the precision required forprobe alignment is lower with larger contact pads than with smallercontact pads.

FIG. 15A depicts a system 1500 for contacting a wafer 1502 for testing.The wafer 1502 includes multiple ICs, only one of which is labeled. IC1504 includes two contact pads 1506 and 1508. A probe card 1510 includesmultiple test probes, two of which are labeled 1512 and 1514. The testprobes 1512 and 1514 are configured to test IC 1504 by formingelectrical connections with contact pads 1506 and 1508, respectively.The relatively large size of the contact pads 1506 and 1508 allows theprecision with which probe card 1510 is disposed on the wafer 1502 to bereduced, resulting in a reduction of the overall testing time.

FIG. 15B depicts a system 1550 similar to system 1500. In system 1550,probe card 1552 includes probes 1554 and 1556 that may be formed of aflexible, compliant, yet electrically-conductive material. The compliantnature of probes 1554 and 1556 may reduce damage to IC 1504 and/or wafer1502 during testing, as well as improving the electrical connectionbetween individual probes and contact pads. In some embodiments, probecard 1552 itself may also be formed of a compliant material, which mayimprove probe contact to IC contact pads across multiple ICs on thewafer.

ICs as described herein may also be configured and/or implementfunctionalities as described in Patent Cooperation Treaty (PCT)Application PCT/US12/54531, filed on Sep. 10, 2012. The disclosure ofthe aforementioned PCT application is hereby incorporated by referencefor all purposes.

Embodiments also include methods of assembling a tag as describedherein. An economy is achieved in the present document in that a singledescription is sometimes given for both methods according toembodiments, and functionalities of devices made according toembodiments.

Embodiments may be implemented using programs executed by fully orpartially automated tag manufacturing equipment. A program is generallydefined as a group of steps or operations leading to a desired result,due to the nature of the elements in the steps and their sequence. Aprogram is usually advantageously implemented as a sequence of steps oroperations for a processor, such as the structures described above.

Performing the steps, instructions, or operations of a program requiresmanipulation of physical quantities. Usually, though not necessarily,these quantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter and in the more general case can includethe states of any physical devices or elements.

Embodiments may furthermore include storage media for storing theprograms discussed above. A storage medium according to the embodimentsis a machine-readable medium, such as a memory, and is read by aprocessor controlling a tag assembly machine for assembling tagsaccording to embodiments. If a memory, it can be implemented in a numberof ways, such as Read Only Memory (ROM), Random Access Memory (RAM),etc., some of which are volatile and some non-volatile.

According to some examples, a Radio Frequency Identification (RFID) tagprecursor may include an assembly having an RFID integrated circuit(IC), a nonconductive repassivation layer on a surface of the IC andconfined within a perimeter of the surface, and a conductiveredistribution layer on the repassivation layer and confined within theperimeter of the surface. A first portion of the redistribution layermay be electrically connected to the IC through a first opening in therepassivation layer.

The RFID tag precursor may also include a substrate having a firstantenna terminal, an etchant forming a second opening in a nonconductivebarrier present on the first antenna terminal and/or the first portionof the redistribution layer, and an adhesive attaching the assembly tothe substrate. A first electrical connection may be formed between thefirst antenna terminal and the first portion of the redistribution layerthrough the second opening, and the first opening and the second openingmay be nonoverlapping.

According to another example, a method for assembling an RFID tagprecursor may include providing an assembly having an RFID IC, anonconductive repassivation layer on a surface of the IC and confinedwithin a perimeter of the surface, and a conductive redistribution layeron the repassivation layer and confined within the perimeter of thesurface. A first portion of the redistribution layer may be electricallyconnected to the IC through a first opening in the repassivation layer.

The method may further include providing a substrate having a firstantenna terminal, forming a second opening in a nonconductive barrierpresent on the first antenna terminal and/or the first portion of theredistribution layer with an etchant, where the first and secondopenings are nonoverlapping, attaching the assembly to the substratewith an adhesive, and forming a first electrical connection between thefirst antenna terminal and the first portion of the redistribution layerthrough the second opening.

According to yet another example, a Radio Frequency Identification(RFID) tag precursor may include an assembly having an RFID integratedcircuit (IC), a nonconductive repassivation layer on a surface of the ICand confined within a perimeter of the surface, and a conductiveredistribution layer on the repassivation layer and confined within theperimeter of the surface. A first portion of the redistribution layermay be electrically connected to the IC through a first opening in therepassivation layer.

The RFID tag precursor may also include a substrate having a firstantenna terminal, a reactant reacting with a portion of a nonconductivebarrier present on the first antenna terminal and/or the first portionof the redistribution layer, and an adhesive attaching the assembly tothe substrate. The reacted portion of the nonconductive barrier may beconductive, and a first electrical connection may be formed between thefirst antenna terminal and the first portion of the redistribution layerthrough the reacted portion.

According to some embodiments, the redistribution layer may be patternedsuch that portions that have a local parasitic capacitance to the ICthat exceeds a predefined threshold are excised. The nonconductivebarrier may be an oxide or a masking layer. The adhesive may include ananisotropic or isotropic conductive material, and the first electricalconnection may include the adhesive. The etchant may include a texturedsurface on the redistribution layer and/or conductive particles thatforms the second opening by breaking the nonconductive barrier. Theetchant may form the second opening by reacting with the nonconductivebarrier. In some embodiments, the substrate may also include a secondantenna terminal, the redistribution layer may include a second portionelectrically isolated from the first portion and electrically connectedto the IC, the nonconductive barrier may be present on the secondantenna terminal and/or the second portion of the redistribution layer,the etchant may form a third opening in the nonconductive barrier, and asecond electrical connection may be formed between the second antennaterminal and the second portion of the redistribution layer through thethird opening.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theembodiments. Although the subject matter has been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims and embodiments.

We claim:
 1. A method to assemble a Radio Frequency Identification(RFID) tag precursor, the method comprising: providing an assemblyhaving an RFID integrated circuit (IC), a nonconductive repassivationlayer on a surface of the IC and confined within a perimeter of thesurface, and a conductive redistribution layer on the repassivationlayer and confined within the perimeter of the surface, in which a firstportion of the redistribution layer is electrically connected to the ICthrough a first electrical connection; attaching, with an adhesive, asubstrate having a first antenna terminal to the assembly; reacting,with a reactant, at least a first portion of a nonconductive barrierpresent on at least one of the first antenna terminal and the firstportion of the redistribution layer to make the first portion of thenonconductive barrier conductive; and forming a second electricalconnection between the first antenna terminal and the first portion ofthe redistribution layer through the first portion of the nonconductivebarrier.
 2. The method of claim 1, wherein the first electricalconnection includes an opening in the repassivation layer.
 3. The methodof claim 2, wherein the opening and a first portion of the nonconductivebarrier are nonoverlapping.
 4. The method of claim 2, wherein theopening and at least a portion of a first portion of the nonconductivebarrier are nonoverlapping.
 5. The method of claim 1, wherein thenonconductive barrier is at least one of an oxide and a masking layer.6. The method of claim 1, wherein the adhesive includes the reactant. 7.The method of claim 1, wherein: the substrate further includes a secondantenna terminal; the redistribution layer further includes a secondportion electrically isolated from the first portion and electricallyconnected to the IC; the nonconductive barrier is further present on atleast one of the second antenna terminal and the second portion of theredistribution layer; and the method further comprises forming a thirdelectrical connection between the second antenna terminal and the secondportion of the redistribution layer through a second portion of thenonconductive barrier made conductive by a reaction with the reactant.